1. Field of the Invention
The present invention relates to an angle adjusting device, and more particularly to an angle adjusting device for a chair to adjust the backrest angle relative to the seat.
2. Description of Related Art
With reference to FIG. 6, a conventional chair adjusting device (50) is adapted to be mounted between a seat (A) and a backrest (B) to allow the backrest (B) to change its angle relative to the seat (A).
With reference to FIGS. 7 and 8, the adjusting device (50) includes a fixed plate (51) adapted for engaging with the seat (A) of the chair and a moving plate (52) adapted for engaging with the backrest (B) of the chair. Furthermore, a U-shaped fixed frame (511) is fixed in the front portion of the fixed plate (51) and a U-shaped moving frame (512) is connected to the bottom of the moving plate (52). Two arcuate slots (513) are respectively and oppositely defined in a side face of the fixed frame (511) and two through holes (514) are also respectively and oppositely defined in the side face of the fixed frame (511) to receive therein a first pin (515) which extends into a mediate portion of the moving plate (52). A second pin (516) is received in the two arcuate slots (513) and is extended into the bottom portion of the moving plate (52). A post (518) has a first distal end securely connected to the fixed frame (511) and a second distal end securely connected to the second pin (516). A spring (517) is sandwiched between the fixed frame (511) and the moving frame (512).
When the conventional adjusting device is in application, that is, the operator is sitting on the chair and leaning on the backrest to apply a force to the moving plate (52), the moving plate (52) is pivoted about the first pin (515) and the bottom portion of the moving plate (52) moves along the arcuate slots (513) due to the second pin (516) being extended into the bottom portion of the moving plate (52) and received in the arcuate slots (513). Meanwhile, due to the movement of the bottom portion of the moving plate (52), the moving frame (512) moves toward the fixed frame (511), which compresses the spring (517) in a longitudinal direction of the post (518) to provide a damping effect to the force to the moving plate (52) so that the operator is able to slowly stretch out in a slanted position when the angle between the moving plate (52) and the fixed plate (511) becomes bigger and bigger.
However, the inclination of the moving plate (52) depends entirely on the force applied to the moving plate (52). That is, if the force applied to the moving plate (52) is removed, the moving plate (52) will be sprung back to its original position, which means that the adjusting device can not provide a positioning mechanism to maintain the position of the moving plate (52) relative to the fixed plate (511) and the operator will have to apply a force to the moving plate (52) every time the operator wants to have a relaxed sitting position.
In order to overcome the conventional drawback, a manufacturer introduced another kind of adjusting mechanism.
With reference to FIGS. 9 and 10, a different conventional adjusting device (60) is shown and has a fixed plate (61) adapted for engagement with the seat (A) of the chair and a moving plate (62) adapted for engagement with the backrest (B). The fixed plate (61) has an arcuate slot (611) defined in opposite sides of the fixed plate to receive therein a first pin (612) which extends into the bottom portion of the moving plate (62). A second pin (613) is provided to extend through the opposite sides of the fixed plate (61) and into a mediate portion of the moving plate (62) to allow the moving plate (62) to pivot relative to the fixed plate (61) using the second pin (613) as the pivotal center.
A shaft (613a) is pivotally connected to the first pin (612) and is extended through a housing (614) securely formed inside the fixed plate (61) and is mounted with a spring (615). Two limiting blocks (616) are also loosely mounted on the shaft (613a) and received in the housing (614) to be abutted by the spring (615) such that due to the abutment of the spring (615), one side face of each of the limiting blocks (616) is slanted inside the housing (614). A control rod (617) is extended from a side of the fixed plate (61) and into the housing (614). An extension (618) is axially formed on the control rod (617) to selectively engage with the side face of one of the limiting blocks (616). Therefore, when the operator is operating the control rod (617) to drive the extension (618) on the control rod (617) to engage with the side face of one of the limiting blocks (616) so as to render horizontal the slanted side face of the limiting block (616), the moving plate (62) is able to move relative to the fixed plate (61). When the angle of the moving plate (62) reaches a satisfactory position, the operator releases the control rod (617) to allow the side face of the limiting block (616) to be obliquely positioned again. Therefore, due to the slanted side face of the limiting block (616), the shaft (613a) is blocked from movement relative to the housing (614), which prevents the moving plate (62) from movement. Thus, the slanted angle of the moving plate (62) is maintained.
With the description above, it is noted that although the slanted angle of the moving plate (62) is able to be maintained, the complex and complicated structure make the manufacture cost high and repairs hard to carry out due to too many involved elements.
To overcome the shortcomings, the present invention tends to provide an improved angle adjusting device for a chair to mitigate the aforementioned problems.
The primary objective of the present invention is to provide an improved angle adjusting device for a chair, with which the manufacture cost is greatly reduced when compared with the conventional one.
Another objective of the present invention is to provide a cylinder inside the angle adjusting device to provide the damping effect required when the backrest is inclined relative to the seat.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.